Group III nitride semiconductors such as GaN, AlN, AlxGa1-xN (0<x<1), and the like have superior semiconductor properties and are therefore suitable for a substrate of a semiconductor device. Such group III nitride semiconductors are expensive. Therefore, in order to reduce the cost of manufacturing a semiconductor device, there has been proposed a substrate of a semiconductor device, specifically a semiconductor substrate in which a film of a group III nitride semiconductor such as GaN, AlN, or the like is formed on a support substrate such as silicon substrate.
For example, Japanese Patent Laying-Open No. 2006-210660 (PTD 1) discloses a method for manufacturing a semiconductor substrate including the steps of: implanting ions into a front surface and its vicinity of a first nitride semiconductor substrate made from GaN, AlN, or the like; superposing a second substrate on the front surface of the first nitride semiconductor substrate; heat-treating the two substrates superposed on each other; and stripping most of the first nitride semiconductor substrate from the second substrate along a layer in which the ions are implanted.